U.S. patent number 4,117,054 [Application Number 05/780,425] was granted by the patent office on 1978-09-26 for method of compensating for the roll deflection in a calender.
This patent grant is currently assigned to Oy Wiik & Hoglund Ab. Invention is credited to Esko Salo.
United States Patent |
4,117,054 |
Salo |
September 26, 1978 |
**Please see images for:
( Certificate of Correction ) ** |
Method of compensating for the roll deflection in a calender
Abstract
The method maintains a set nip clearance at a uniform value
across the widths of the calendar, at different calendar loads, in
at least the last nip, in the working direction, of a calender
stack or the like including at least three rolls subjected to a
common work-press load, with at least one roll being crowned to
correspond to the maximum load of the calendar and at least one
roll being adjustable. The thickness of the material being treated
is sensed at one or several points in a direction transverse to the
material web, or the deflection, or the load, is sensed at one or
several of the rolls. The position of one or more adjustable rolls
is displaced, relative to the common plane through the roll axes,
in accordance with the sensing in a manner such that the axis of
the adjustable roll or rolls remains parallel to the adjacent roll
axis. The adjustable rolls may be displaced horizontally either
linearly or arcuately to follow the contour of the adjacent rolls.
The adjustment may be effected automatically responsive to
measurements and to calculations performed by a computer.
Inventors: |
Salo; Esko (Jakobstad,
FI) |
Assignee: |
Oy Wiik & Hoglund Ab
(FI)
|
Family
ID: |
8509871 |
Appl.
No.: |
05/780,425 |
Filed: |
March 23, 1977 |
Foreign Application Priority Data
Current U.S.
Class: |
264/40.1; 100/35;
100/168; 264/175; 425/363; 72/248; 100/47; 264/40.5; 425/172;
425/367 |
Current CPC
Class: |
D21G
1/0033 (20130101); B29C 43/245 (20130101); B29B
7/68 (20130101); B21B 13/14 (20130101) |
Current International
Class: |
B21B
13/14 (20060101); B29C 43/24 (20060101); D21G
1/00 (20060101); B29B 7/68 (20060101); B29B
7/30 (20060101); B29C 015/00 (); B29D 009/02 ();
B29D 007/14 () |
Field of
Search: |
;264/40.1,40.5,175
;425/172,363,367 ;100/35,47,168 ;72/248 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hoag; W.E.
Attorney, Agent or Firm: McGlew and Tuttle
Claims
I claim: 3
1. A method for adjusting spacing, across the full width of a
calendar stack, between at least rolls defining the last nip of a
calendar stack having at least 3 rolls subjected to a common
work-pressing load, less than a predetermined maximum value, axes
of at least two of said rolls lying in a common plane, said method
comprising: crowning at least one roll of said three one roll of
the stack. rolls to correspond to said maximum work load for said
stack; for work loads less than said maximum, correcting for excess
crowning of said one roll, by displacing at least one of said rolls
forming said nip relative said common plane in such a way as to
initially change spacing between the crowned roll and a remaining
two of said at least three rolls while maintaining parallel the
axes of said at least three rolls, and moving said two rolls toward
each other in said plane to compensate for said displacement of
said one roll.
2. A method, as claimed in claim 1, in which each crowned roll is
displaced relative to such common plane.
3. A method, as claimed in claim 1, in which the rolls adjacent a
crowned roll are displaced relative to such common plane.
4. A method as claimed in claim 1, in which each adjustable roll is
displaced linearly.
5. A method, as claimed in claim 1, comprising crowning one of the
rolls defining the last nip of the stack.
6. A method, as claimed in claim 1, in which each roll displaceable
relative to such common plane is displaced based on one of such
sensings and on calculations performed by a computer.
7. The method of claim 1, wherein the axis of each displeasable
roll is displaced relative the common plane in an arcuate path.
8. A method as in claim 1 wherein each of the rolls displaceable
relative the common plane is displaced in response to sensing
thickness of the calendared web at least one point transversely of
its width.
9. A method as in claim 1, wherein each of the rolls displaceable
relative the common plane is displaced in response to sensing
deflection of at least one roll of the stack.
10. A method as in claim 1, wherein each of the rolls displaceable
relative the common plane is displaced in response to sensing the
load of at least one roll of the stack.
Description
The present invention concerns primarily a method of obtaining a
substantially even profile along the whole roll width irrespective
of the roll deflection at least in the last nip of a calender stack
in the direction of movement of the web, and thus an even material
thickness along the whole web width.
BACKGROUND OF THE INVENTION
A major problem of the calenders used, e.g. in the plastic industry
for the manufacture of thin plastic foils or films, has been the
deflection of the rolls, especially the long rolls, which
deflection varies at adjacent rolls and thus gives rise to
variations in the roll nip in a direction transverse to the roll
assembly. This naturally also gives rise to irregularities and
variations in the foil profile in a direction transverse to the
manufactured web, above all variations in the thickness. The
negative effect of the uneven profile is especially apparent in
thin plastic webs. An uneven foil is also difficult to use.
Different means have been used in an attempt to eliminate the above
mentioned disadvantages caused by the roll deflection. Attempts
have been made i.a. to bend the roll in the opposite direction to
counteract the deflection. This is achieved by applying a load on
the roll axis at both ends outside the bearing points, which load
opposes the pressing force. In this way it is possible to
compensate for the deflection of the adjacent roll to some degree,
but not entirely, and this results in an oxbow profile of the
mmaterial to be treated.
Another method of compensating consists in inclining the roll axis
in relation to the adjacent roll axes, but also in this case the
result is similar, that is an oxbow profile is obtained.
The most advantageous method of compensating for the roll
deflection consists in crowning the rolls in accordance with the
roll deflection. In this way a constant nip width is obtained, but
only if all the factors on which the desired crowning is based,
i.e. the working speed of the calender, the composition of the
material and the temperature and material thickness etc., remain
unchanged. If one of these factors is changed, also the crowning of
the roll should be corrected. This is, however, very difficult to
carry out in practice.
It is also known to adjust the roll thickness at certain areas
along the rolls by alternatively heating or cooling the areas in
question, as required.
Finally also so called "non-bending" rolls exist which are very
expensive, but not even the characteristics of these rolls are
sufficient to cover completely all existing fields of
application.
SUMMARY OF THE INVENTION
The object of the invention is to provide a practically applicable
method of compensating for such variations, in the thickness along
the width of the material web, which are caused by the roll
deflection, when the load conditions in the calender change, and
tests have shown that a constant nip width may be achieved at least
in the last nip in the direction of web movement, which is of
extreme importance as this nip imparts the web with its final
thickness profile.
In an ordinary calender or a roll assembly the rolls are usually
arranged one on top of the other, or at least in such a way that
the axis ends normally are aligned, except the above mentioned
inclination of one of the rolls. The pressing load on the rolls and
also the load exerted by the weight of the roll are oriented along
this straight line defined by the axes ends. The invention resides
in the discovery that the irregularities in the nip caused by the
roll deflection first are eliminated by crowning at least one of
the rolls to correspond to certain predetermined calender
conditions which give a maximum working load, and that the
variations in the roll deflection caused by changes in the varying
factors which decrease the load in the calender thereafter are
eliminated by allowing controlled deflection of an adjustable roll
or rolls so that a constant nip width value along the whole nip
length is achieved. This is achieved by resolving the pressing and
weight loads acting on the adjustable roll or rolls into components
by displacing the roll or rolls, whereby the force component acting
on the nip may be adjusted to a constant value whose magnitude is
so exact as to give a constant width along the whole nip length. As
a result of the displacement, the adjustment roll is deflected and
thus the excess crowning eliminated.
The characteristic features of the invention appear from the
appended claims.
The adjusting of the calender may be carried out manually but the
invention method has proved especially advantageous in connection
with automatic calender adjustment whereby the profile of the web
treated or to be treated is sensed at the center of the web and at
its border or borders during the calendering operation. In case the
thickness at the borders differs from the thickness at the center,
the position of the adjustable roll or rolls, respectively, is
changed so as to eliminate the differences in the thickness. This
adjustment is advantageously carried out by means of e.g. a
computer, which has been programmed according to an operational
scheme based on mathematical calculations, and which gives an
instruction to the displacing means of the roll or rolls,
respectively, to effect a parallel displacement of the roll or
rolls in accordance with the measuring results obtained. Another
possibility of informing, e.g. a computer for the purpose of
adjusting the roll position, consists in sensing the surface of the
adjustable roll or rolls, respectively, at the center and at the
ends, i.e. to measure the magnitude of deflection, and to transfer
the result to a computer to calculate the magnitude of the
displacement required. The adjusting impulse may also be received
from means measuring the roll pressure.
The adjustable roll or rolls may be displaced either linearly or
along an arcuate line following the outer surface of the adjacent
roll, but the displacement should always take place in such a way
that the roll axes remain mutually parallel. When the adjustable
roll is displaced from its original position further away from the
line connecting the center line of the adjacent roll axes, these
two latter rolls move towards each other a distance corresponding
to the space left free by the outwardly displaced roll. For an
understanding of the principles of the invention, reference is made
to the following description of typical embodiments thereof as
illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a somewhat schematic side elevation view of a calendar
comprising four rolls;
FIG. 2 diagrammatically illustrates the forces acting on the nips
and the bearings and the direction and magnitude of these
forces;
FIG. 3 is the force diagram showing the magnitude of the horizontal
displacement of an adjustable roll compensating for half of the
maximum load in a calendar where the last and the second-last rolls
are of equal thickness; and
FIGS. 4, 5 and 6 are views, simmilar to FIG. 1, illustrating
alternative embodiments of the invention method.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a calender for plastic foils comprising four rolls.
The plastic material is fed into the nip between the first two
rolls 1,2 from which the foil moves along the rolls 2,3 and 4 and
along one part of their surfaces whereby the thickness of the foil
decreases in the nips between these rolls and leaves the machine as
a web 5. In the embodiment shown, the roll 3, or rolls 3 and 4, are
crowned so that the calender produces an even foil web under
certain predetermined working conditions under maximum load. When
one or more of these conditions change, e.g. when the load on the
nip between the rolls 3 and 4 decreases, the roll 3 is displaced
horizontally so that the angle A is changed. Thereby a mutual
adjustment of the force components acting on the bearings and the
nips between the rolls is achieved, the nip component remaining
constant and corresponding to the value which formed the basis for
the calculations of the degree of crowning of the rolls. The
bearings of the rolls 2 and 4, or possibly only one of these, are
of course to be designed so as to allow a vertical movement of this
or these rolls. The roll 3 may also be displaced along an arcuate
line, e.g. along a path corresponding to the curvature of the roll
4. The displacement naturally always has to take place so that the
axis of the roll 3 remains parallel to the other roll axes.
FIG. 2 demonstrates the forces acting on the nips and the bearings
and also the direction and magnitude of these forces in a given
position of the roll 3.
FIG. 3 is a force diagram showing the magnitude of the horizontal
displacement of the roll 3 which compensates for the half of the
maximum load in a calender where the last and the second last rolls
are of equal thickness, and in a case where the diameter of the
last roll 4 is 550 mm and the diameter of the second last
displacable roll is 350 mm. In the latter case, besides the angular
displacement .alpha., also the horizontal displacement S has been
calculated.
As is evident from FIGS. 2 and 3, the force 2 F sin.sup.2 .alpha.
is the force acting on the nip between the rolls 3 and 4 and
causing a deflection of the sideways displaced roll 3 in a
direction away from the nip. Consequently this force component is
the one which is adjusted by displacing the roll 3 so that the
deflection in a direction outward from the nip of the displaced
roll 3 compensates for the excess crowning of the roll 3 or 4,
which excess crowning is a result of a decreased load on the
calender.
Although the example shown concerns a calender where only one of
the rolls is horizontally adjustable, it is of course possible to
adapt the method so as to adjust two or more of the calender rolls
in the suggested manner. By spreading the adjustment over several
rolls, the individual limits for the respective displacements may
be kept relatively narrow, it still being possible to achieve a
total adjusting effect which covers a rather wide adjusting area,
and as calenders comprise an integrated system of rolls under
common load, it is evident that an achieved change in the
deflection of one of the rolls leads to a change in the deflection
also in the remaining rolls of the system.
A further mode of the invention is shown in FIGS. 4 to 6. In this
mode two rolls on the same level in the calender are displaced in
pairs sideways, which rolls may be situated at one end of the
calender or possibly at both ends of the calender. Also in this
mode either the roll 3 or the rolls 4',4", or all the rolls
3,4',4", and in the mode of invention of FIG. 6 the corresponding
rolls at one end of the calender are crowned. The roll or rolls are
crowned in such a way that it results in a constant value
transverse to the web in at least the last nip in the direction of
web movement (for example between rolls 2 and 3) and corresponds to
the maximum working load.
In case the load in the calender for some reason has to be
decreased or decreases, for example when the foil to be
manufactured is of the same thickness as before, but softer, the
rolls 4',4" and, with these, also the roll 3 will not deflect
according to the maximum load and consequently the roll 3 will be
excessively crowned, i.e. too thick at the center, which results in
that the foil undergoing treatment in the nip 3-2 will be thinner
at the center compared to the borders. According to the invention
the rolls 4',4" are then displaced in a direction away from each
other in the horizontal plane, allowing space for the roll 3 to
deflect downwardly, whereby the nip between the rolls 3 and 2
increases in size at the center as the roll 3 controllably deflects
downwards to an extent corresponding to the excess crowning. A
similar adjusting system may naturally be provided at both ends of
the calender and the number of interposed rolls in the system may
vary freely.
The method according to the invention has here been described in
connection with the plastic industry, but it is evident that it
equally well may be adapted i.a. in the paper industry and in the
metal industry according to the embodiments shown, e.g. when
manufacturing aluminium webs having a constant profile along the
whole web width.
* * * * *